An ad for Bayer's One A Day Men's notes that there are more new cases of prostate cancer every year than of any other type of cancer. But, the commercial adds, "Now there's something that you can do that may help reduce your risk. Along with your regular doctor checkups, switch to One A Day Men's, a complete multivitamin plus selenium, which emerging research suggests may reduce the risk of prostate cancer."

But CSPI points out that studies have debunked the notion that selenium supplements offer such protection against prostate cancer; in fact, one study showed that they may contribute to some men's developing diabetes.

Selenium is an antioxidant, a compound found in many fruits, vegetables and other foods that many scientists and nutritionists believe helps keep cells healthy and fight such diseases as cancer. But as I have written, nobody really knows how, or even whether, antioxidants really benefit the body. Nor do we know whether antioxidants delivered via supplements, as in the One A Day vitamins, work the same way they might when delivered via the foods in which they naturally occur.

For my part, I'm wary of any packaged product that trumpets its antioxidant content, and I don't buy the health claims attached to any such product. I'll take my chances that my body gets all the antioxidants it needs from the fruits and vegetables I eat every day.